Light emitting device

ABSTRACT

An embodiment of present invention discloses a light-emitting device comprising a first multi-layer structure comprising a first lower layer; a first upper layer; and a first active layer able to emit light under a bias voltage and positioned between the first lower layer and the first upper layer; a second thick layer neighboring the first multi-layer structure; a second connection layer associated with the second thick layer; a connective line electrically connected to the second connection layer and the first multi-layer structure; a substrate; and two or more ohmic contact electrodes between the first multi-layer structure and the substrate.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 12/320,085, filed Jan. 16, 2009 now U.S. Pat. No. 7,816,695, whichis a continuation of Ser. No. 11/550,332, filed Oct. 17, 2006, now U.S.Pat. No. 7,488,988, and for which priority is claimed under 35 USC §120of which the entire disclosure of the pending, prior application ishereby incorporated by reference, and claims the right of priority ofTaiwan Patent Application No. 094136683 filed on Oct. 20, 2005 herebyincorporated by reference.

TECHNICAL FIELD

The present invention generally relates to a light emitting device, andmore particularly to a wafer-level wired light emitting device and amethod of forming the same.

BACKGROUND OF THE INVENTION

Light emitting diodes (LEDs), because of their unique structure andcharacter of emitting lights, are different from those conventionallight sources, and are more versatile for different applications. Forexample, LEDs are characterized in small size, high reliability, andhigh output, so they are suitable for many kinds of devices, such asindoor or outdoor large displays. Compared to conventional tungstenlamps, the LEDs are widely applied to communication devices orelectronic devices because they work without a filament, consume lesspower, and respond more quickly. Furthermore, white LEDs have a betterlight-emitting efficiency, a longer lifetime, no harmful material likemercury, a smaller size, and lower power consumption, and therefore theLED devices are advancing in the lighting market.

Conventionally, after the fabrication of an LED wafer is completed, thewafer is cut into many LED chips. The LED chips are then arranged on apre-designed circuit board to accomplish the manufacture of lightemitting devices based on different needs. However, when the LED chipsare individually wired by wire-bonding technique, the fabricationprocess is complicated and the conductive wire is susceptible tobreakage. Consequently, the production yield is low and the cost ishigh.

Therefore, there is a need to provide a light emitting device and amethod of forming the same so as to improve the bonding quality and toreduce the fabrication cost.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a light emitting device,which includes a plurality of light emitting diode structures wired inwafer level to form the LEDs connected in series or in parallel so as toimprove the yield and reduce the manufacture cost.

In one embodiment, the present invention provides a light emittingdevice which includes a substrate, an adhesive layer on the substrate,and a first multi-layer epitaxial structure and a second multi-layerepitaxial structure on the substrate. Each of the multi-layer epitaxialstructures has a light emitting structure including an upper claddinglayer, an active layer, a lower cladding layer, an ohmic contactepitaxial layer on the upper cladding layer, a first ohmic contactelectrode on the ohmic contact epitaxial layer adhered to the substrateby the adhesive layer. A second ohmic contact electrode is on the lowercladding layer. A trench is formed within the light emitting structureto divide the active layer into a first portion and a second portion. Afirst electrode is on the lower cladding layer corresponding to thefirst portion of the active layer. A second electrode is on the secondohmic contact electrode corresponding to the second portion of theactive layer. A connection layer formed in the light emitting structureand the first ohmic contact epitaxial layer couples the first electrodeand the first ohmic contact electrode. A dielectric layer is between thefirst and the second multi-layer epitaxial structures. A conductive linecouples the first electrode of one of the two multi-layer epitaxialstructures to the first electrode or the second electrode of the otherone of the first and the second multi-layer epitaxial structures.

It is a further object of this invention to provide a method for forminga light emitting device, which integrates the wiring process of aplurality of light emitting diodes into the wafer fabrication to avoidthe complicated processes of individual chip dicing, wire bonding, andconnection.

In an alternative embodiment, the present invention provides a methodfor forming a light emitting device, which comprises providing atemporary substrate, forming a multi-layer epitaxial layer on thetemporary substrate. The steps of forming the multi-layer epitaxiallayer comprise forming a lower cladding layer on the temporarysubstrate, forming an active layer on a lower cladding layer, forming anupper cladding layer on the active layer, and forming an ohmic contactepitaxial layer on the upper cladding layer. The method further includesforming a plurality of first ohmic contact electrodes on the ohmiccontact epitaxial layer, providing a substrate, forming an adhesivelayer on the substrate, connecting the multi-layer epitaxial layer andthe substrate by the adhesive layer so that the first ohmic contactelectrode is between the ohmic contact epitaxial layer and thesubstrate, removing the temporary substrate to expose the lower claddinglayer, forming a plurality of connection layers in the multi-layerepitaxial layer, forming a plurality of trenches in the multi-layerepitaxial layer to separate the active layer into a plurality of firstportions and a plurality of second portions, forming a plurality ofsecond ohmic contact electrodes on the lower cladding layer, forming aplurality of first electrodes on the lower cladding layer, the firstelectrode corresponding to the first portion of the active layer, andcoupled to the first ohmic contact electrode by the connection layer,forming a plurality of second electrodes on the second ohmic contactelectrode, the second electrode corresponding to the second portion ofthe active layer, removing a portion of the multi-layer epitaxial layerto form at least two independent multi-layer epitaxial structures, eachof the multi-layer epitaxial structures having a first electrode and asecond electrode, forming a dielectric layer between the two multi-layerepitaxial structures, and forming a conductive line coupling the firstelectrode of one of the two multi-layer epitaxial structures to thefirst electrode or the second electrode of the other one of the twomulti-layer epitaxial structures.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same becomesbetter understood by reference to the following detailed description,when taken in conjunction with the accompanying drawings, wherein:

FIG. 1A and FIG. 1B are schematic views of a multi-layer epitaxial layeron a temporary substrate in accordance with different embodiments of thepresent invention;

FIG. 2 is schematic view of an exemplary substrate of the presentinvention;

FIG. 3A and FIG. 3B are schematic views of bonding the structures ofFIG. 1A and FIG. 1B to an exemplary substrate in accordance with thepresent invention;

FIG. 4 is schematic view of the multi-layer epitaxial layer bonded tothe substrate in accordance with the present invention;

FIGS. 5A-9A illustrate a process flow of forming a light emitting devicein accordance with an embodiment of the present invention; and

FIGS. 5B-9B illustrate a process flow of forming a light emitting devicein accordance with another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a light emitting device and a methodthereof, wherein a plurality of light emitting diodes are wired inseries or in parallel according to different design requirements duringwafer fabrication. Therefore, a complicated fabrication process ofindividual chip dicing, wire bonding, and connection can be avoided toimprove the yield and to decrease the manufacture cost. The presentinvention will now be described in detail with reference to FIGS. 1 to9.

The preferred embodiments of the present invention are illustrated inFIG. 9A and FIG. 9B. Referring to FIG. 9A, the light emitting deviceincludes a substrate 200, an adhesive layer 210 on the substrate 200,and multi-layer epitaxial structure 800A, 800B on the substrate 200.Both multi-layer epitaxial structures 800A and 800B include a lightemitting structure, which includes an upper cladding layer 116, anactive layer 114, and a lower cladding layer 112. An ohmic contactepitaxial layer 118 is on the upper cladding layer 116. A first ohmiccontact electrode 120 is on the ohmic contact epitaxial layer 118. Thefirst ohmic contact electrode 120 is adhered to the substrate 200 by theadhesive layer 210. A second ohmic contact electrode 126 is on the lowercladding layer 112. A trench 124 is formed within the light emittingstructure to separate the active layer 114 into a first portion (I) anda second portion (II). A first electrode 128 is on the lower claddinglayer 112 and corresponds to the first portion (I) of the active layer114. A second electrode 130 is on the second ohmic contact electrode 126and corresponds to the second portion (II) of the active layer 114. Aconnection layer 122 is formed in the light emitting structure and thefirst ohmic contact epitaxial layer 118 and to couple the firstelectrode 128B and the first ohmic contact electrode 120. A dielectriclayer 90 separates the multi-layer epitaxial structure 800 into thefirst multi-layer epitaxial structure 800A and the second multi-layerepitaxial structure 800B. A connective line 92 couples the firstelectrode 128A of the first multi-layer epitaxial structure 800A to thesecond electrode 130B of the second multi-layer epitaxial structure 800Bto form a series connection. In another embodiment, as shown in FIG. 9B,the connective line 92 couples the first electrode 128A of the firstmulti-layer epitaxial structures 800A to the first electrode 128B of thesecond multi-layer epitaxial structures 800B to form a parallelconnection. FIG. 9A and FIG. 9B also illustrate another embodiment ofthe present invention. The multi-layer epitaxial structure 800A includesa second multi-layer structure 900A, a second thick layer 901A and asecond connection layer 123 associated with the second thick layer 901A.The multi-layer structure 800B includes a first multi-layer structure900B, a first thick layer 901B, and a first connection layer 122associated with the first thick layer 901 B. A lower portion 902 isformed between the multi-layer structure 800A and the multi-layerstructure 800B such that the second thick layer 901A neighbors the firstmulti-layer structure 900B and/or the first thick layer 901B, and/or thefirst thick layer 901B neighbors the second multi-layer structure 900Aand/or the second thick layer 901A. A connective line 92 bridges thelower portion 902 to electrically connect the two thick layers and/orthe thick layer and the multi-layer structure. In addition, a dielectriclayer 90 is formed nearby the connective line 92 to electricallydisconnect the connective layer 92 from the thick layer and/or themulti-layer, structure. Preferably, the dielectric layer 90 is formed onone side of the connective line 92, and more preferably, the greaterportion of the dielectric layer 90 is formed on either the multi-layerstructure 800A or the multi-layer structure 800B.

Referring to FIG. 1A, a method for forming a light emitting devicementioned above is disclosed. The method includes a step of providing atemporary substrate 100, which includes an n-type GaAs substrate. Then,a multi-layer epitaxial layer 110 is formed on the temporary substrate100. The steps of forming the multi-layer epitaxial layer 110 includesteps of forming a lower cladding layer 112 on the temporary substrate100, forming an active layer 114 on the lower cladding layer 112,forming an upper cladding layer 116 on the active layer 114, and formingan ohmic contact epitaxial layer 118 on the upper cladding layer 116.The lower cladding layer 112 includes an n-type(Al_(x)Ga_(1-x))_(0.5)In_(0.5)P epitaxial layer, wherein x is between0.5 and 1 (x=0.5˜1). The active layer 114 includes an undoped(Al_(x)Ga_(1-x))_(0.5)In_(0.5)P epitaxial layer, wherein x is between 0and 0.45 (x=0˜0.45). The upper cladding layer 116 includes a p-type(Al_(x)Ga_(1-x))_(0.5)In_(0.5)P epitaxial layer, wherein x is between0.5 and 1 (x=0.5˜1). When the active layer 114 contains no Al (x=0), thecomposition of the active layer 114 is Ga_(0.5)In_(0.5)P, which can emitlights with wavelength of about 635 nm (within the range of visible redlight). Furthermore, the active layer 114 includes the homo-structure,single hetero-structure (SH), double hetero-structure (DH) or multiplequantum well (MQW) structure.

The steps of forming the ohmic contact epitaxial layer 118 include astep of forming a p-type ohmic contact epitaxial layer, which can be aGaP, GaAsP, AlGaAs or InGaP epitaxial layer. The band gap of the ohmiccontact epitaxial layer 118 is higher than that of the active layer 114,so as to reduce the absorption of lights of the active layer 114.Preferably, the ohmic contact epitaxial layer 118 is doped with a highercarrier concentration to form a good ohmic contact.

In another embodiment, as shown in FIG. 1B, it is noted that prior tothe step of forming the multi-layer epitaxial layer 118, an etching stoplayer 105 is selectively formed on the temporary substrate 100 as anover etch protection layer during the removal of the temporary substrate100. The etching stop layer 105 can be a III-V compound semiconductorlayer having a lattice matching with the temporary substrate 100 (suchas GaAs temporary substrate) to reduce the dislocation density, such asInGaP layer or AlGaAs layer. Preferably, the etching stop layer 105 hasan etching rate lower than that of the temporary substrate 100.Alternatively, when the lower cladding layer 112 is thick enough toserve the purpose of an etching stop layer, it is not necessary toadditionally form the etching stop layer 105.

A plurality of first ohmic contact electrodes 120 is then formed on theohmic contact epitaxial layer 118, as shown in FIG. 1A and FIG. 1B. Inthis embodiment, the steps of forming the first ohmic contact electrodeinclude forming a p-type ohmic contact electrode by implementing thedeposition, lithography, and etch processes.

Referring to FIG. 2, a substrate 200 is provided. The substrate 200 canbe a glass substrate, a sapphire substrate, a SiC substrate, a GaPsubstrate, a GaAsP substrate, a ZnSe substrate, a ZnS substrate, and aZnSSe substrate. Then, an adhesive layer 210 is formed on the substrate200. The adhesive layer 210 is selected from a group consisting of thespin-on glass, silicone, BCB (Benzocyclobutene) resin, epoxy, orpolyimide.

Referring to FIG. 3A and FIG. 3B, the multi-layer epitaxial layer 110 isattached to the substrate 200 by using the adhesive layer 210 so thatthe first ohmic contact electrode 120 is between the ohmic contactepitaxial layer 118 and the substrate 200. The attaching step isperformed at an elevated temperature in the range of about 200° C. toabout 600° C. with pressure to tightly attach the multi-layer epitaxiallayer 110 and the substrate 100 together.

Next, the temporary substrate 100 is removed to expose the lowercladding layer 112, as shown in FIG. 4. In this embodiment, the step ofremoving the GaAs temporary substrate 100 includes removing the GaAstemporary substrate 100 by using an etchant, such as the5H₃PO₃:3H₂O₂:3H₂O solution or NH₄OH:35H₂O₂ solution. If the etching stoplayer 105 is optionally implemented (FIG. 3B), the etching stop layer105 is removed to expose the lower cladding layer 112 after the removalof the temporary substrate 100.

A plurality of connection layers 122 is formed in the multi-epitaxiallayer 110. As shown in FIG. 5A and FIG. 5B, the steps of forming theconnection layer 122 include forming a patterned photoresist layer 50 onthe lower cladding layer 112. The patterned photoresist layer 50 definesa plurality of openings 52. The multi-layer epitaxial layer 110 is thenetched to expose the first ohmic contact electrode 120 by using thepatterned photoresist layer 50 as a mask. Then, the patternedphotoresist layer 50 is removed. The openings are filled with aconductive material to form the connection layer 122, as shown in FIG.6A and FIG. 6B. A plurality of trenches is formed in the multi-layerepitaxial layer to divide the active layer 114 into a plurality of firstportions (I) and a plurality of second portions (II). The steps offorming trenches 124 include lithography and etching processes. It isnoted that that the trench 124 is implemented to separate the activelayer 114, and therefore, the etching is down through the lower claddinglayer 112, the active layer 114 and a portion of the upper claddinglayer 116. Alternatively, the etching can proceed further down to aninterface between the upper cladding layer 116 and the first ohmiccontact layer 118 or extend to a portion of the first ohmic contactlayer 118 so as to ensure that the active layer 114 is separated.

As shown in FIG. 7A and FIG. 7B, a plurality of second ohmic contactelectrodes 126 (such as an n-type ohmic contact electrodes) is formed onthe lower cladding layer 112. The steps of forming the second ohmiccontact electrodes 126 include spinning a photoresist layer on theentire structure to fill in the trenches 124. The photoresist layer isexposed and developed to form a patterned photoresist layer, whichdefines the second ohmic contact electrodes 126. A plurality of firstelectrodes 128 is formed on the lower cladding layer 112. The firstelectrode 128 corresponds to the first portion (I) of the active layer114 and couples with the first ohmic contact electrode 120 through theconnection layer 122. Furthermore, a plurality of second electrodes 130is formed on the second ohmic contact electrode 126. The secondelectrode 130 corresponds to the second portion (II) of the active layer114. It is noted that the first electrode 128 and the second electrode130 can be formed individually or simultaneously. For example, a singlelithography process can define a pattern including the first electrodeand the second electrode so as to form the first electrode 128 and thesecond electrode 130 simultaneously.

Referring to FIG. 8A and FIG. 8B, a portion of the multi-layer epitaxiallayer 110 is removed to form at least two independent multi-layerepitaxial structures 800. Each multi-layer epitaxial structure 800includes a first electrode 128 and a second electrode 130. The steps offorming the independent multi-layer epitaxial structure 800 includeforming at least two independent multi-layer epitaxial structures 800 byan etching process or cutting process. The etching depth could be anydepth sufficient to isolate the multi-layer epitaxial structures 800.For example, in this embodiment, the multi-layer epitaxial layer 110 isetched down to expose the adhesive layer 210 since the adhesive layer210 is a non-conductive adhesive layer.

Referring to FIG. 9A and FIG. 9B, a dielectric layer 90 is formedbetween the two multi-layer epitaxial structures 800 to form a firstmulti-layer epitaxial structure 800A and a second multi-layer epitaxialstructure 800B. The dielectric layer 90 includes Al₂O₃, SiO₂, SiNx,spin-on glass, silicone, BCB resin, epoxy, or polyimide. Then, aconductive line 92 (for example, a metal line) is formed to connect thefirst electrode 128A of the second multi-layer epitaxial structure 800Aand the first electrode 128B or the second electrode 130B of the secondmulti-layer epitaxial structure 800B. In other words, the plurality ofmulti-layer epitaxial structures 800 can be connected in parallel or inseries, or both parallel and series according to different designrequirement during a single connection process. Furthermore, the presetinvention eliminates the need of designing an extra printed circuitboard for connecting individual light emitting chips thereon, andaccordingly, the fabrication process is simplified and the manufacturecost is reduced. In addition, the present invention utilizes the waferlevel connection to connect the plurality of multi-layer epitaxialstructures, and accordingly, the device size of the light emittingdevice is smaller than that of a conventional light emitting devicewhich is fabricated by wire bonding.

Though only two multi-layer epitaxial structures in series or inparallel are illustrated in drawings, it is noted that the number andconfiguration of the multi-layer epitaxial structures are not limited tothose illustrated in the embodiments. Nevertheless, the skilled in theart can recognize that various modifications may be made. The pluralityof multi-layer epitaxial structures of the light emitting device can beconnected in series connection, parallel connection, or parallel-seriesconnection.

Although specific embodiments have been illustrated and described, itwill be apparent that various modifications may fall within the scope ofthe appended claims.

1. A light-emitting device, comprising: a first part epitaxial layerhaving a first upmost top surface and a first width; one or more secondpart epitaxial layers, each second part epitaxial layer, laterallyseparated from the first part epitaxial layer, able to emitting lightunder a forward bias voltage and having a second upmost top surface anda second width; and an underlayer formed below the first upmost toplayer and the each second upmost top layer, and electrically connectedto the first part epitaxial layer and the each second part epitaxiallayer; wherein the first upmost top layer has an elevation substantiallyequal to that of the second upmost top surface, and the first width issubstantially equal to the second width.
 2. The light-emitting device ofclaim 1, wherein the first part epitaxial layer and the one or moresecond part epitaxial layers are electrically connected in seriesconnection.
 3. The light-emitting device of claim 1, wherein the firstpart epitaxial layer can flow current through a current path inside thefirst part epitaxial layer when the forward bias voltage is applied tothe one or more second part epitaxial layers.
 4. The light-emittingdevice of claim 1, further comprising a first connection layerassociated with the first part epitaxial layer.
 5. The light-emittingdevice of claim 1, further comprising a first electrode formed on thefirst upmost top surface.
 6. The light-emitting device of claim 1,further comprising an ohmic contact electrode formed below theunderlayer.
 7. The light-emitting device of claim 1, further comprisinga non-conductive layer formed below the underlayer.
 8. Thelight-emitting device of claim 1, further comprising a substrate formedbelow the underlayer.
 9. The light-emitting device of claim 1, whereinthe first part epitaxial layer comprises a connection layer formed toextend a thickness of the first epitaxial structure.
 10. Thelight-emitting device of claim 1, further comprising: a trench formednearby one side of the first part epitaxial layer; and a lower portionformed nearby another side of the first part epitaxial layer, and beingdeeper than the trench.
 11. A light-emitting device, comprising: a firstepitaxial structure, comprising: a first part epitaxial layer having afirst upmost top surface and a first width; and a second part epitaxiallayer, laterally separated from the first part epitaxial layer, able toemitting light under a forward bias voltage and having a second upmosttop surface and a second width; a second epitaxial structureelectrically connected to the first epitaxial structure, comprising: afourth part epitaxial layer able to emitting light under the forwardbias voltage, and having a fourth upmost top surface and a fourth width;and a lower portion laterally separating the first epitaxial structureand the second epitaxial structure; wherein the first width issubstantially equal to the second width.
 12. The light-emitting deviceof claim 11, wherein the first epitaxial structure and the secondepitaxial structure are electrically connected in series connection orparallel connection.
 13. The light-emitting device of claim 11, whereinthe first part epitaxial layer can flow current through a current pathinside the first part epitaxial layer when the forward bias voltage isapplied to the one or more second part epitaxial layer.
 14. Thelight-emitting device of claim 11, wherein the second epitaxialstructure further comprises a third part epitaxial layer laterallyseparated from the fourth part epitaxial layer and having a third upmosttop surface and a third width.
 15. The light-emitting device of claim14, wherein the third width is substantially equal to the fourth width.16. The light-emitting device of claim 14, wherein the third width issubstantially equal to the first width.
 17. The light-emitting device ofclaim 14, wherein at least two of the four upmost top surfacessubstantially have the same elevation.
 18. The light-emitting device ofclaim 14, wherein at least one of the epitaxial structures furthercomprises a trench laterally separating the two part epitaxial layers.19. The light-emitting device of claim 18, wherein the lower portion isdeeper than the trench.
 20. The light-emitting device of claim 11,further comprising a first connection layer associated with the firstpart epitaxial layer.